> I suppose, but wouldn't it read high anyway?  The ones 
> that go bang would be
> really high.  A bit moot as I don't have an ESR meter.

Easy ESR tester.

Square wave source at V around 1 Volt.
Lower the impedance the better.
(Having a stiff enough source to not be loaded too much by 
ESR + resistor load helps brain when calculating.)
Series resistor to test point - value maybe a bit above 
expected ESR levels.
Oscilloscope at test point.

Observe waveform at each end of resistor (or across resistor 
and at one end or whatever works for you).

When square waveform steps it will initially be constrained 
only by the ESR/resistor ratio.
Ignore what happens from then on until next transition as it 
will be affected by capacitor value.
Apply Ohms law.

IF source drops under load apply intelligent processing of 
readings.

Vstep/Vsignal = ESR/(ESR+Series_R)
or for Vstep/Vsignal = k

    ESR = kR/(1-k)


eg Assuming stiff 1 volt square wave.
Series 4R resistor (nice simple arithmetic)
If cap voltage steps by 0.2 Volts at transition then

k = 0.2/1 = 0.2
ESR =  kR/(1-k) = 0.2 x 4 / (1-0.2) = 1 ohm.

E&OE.

This can be very useful in testing a large number of similar 
items or for a specific situation as a relative change on 
ESR will be easily noticed.



        Russell


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